Take the following piece of code as an example:
In this example, the 2-dimensional instantiation label and_inst[1:0][1:0] in the array of instances causes the 13.3 XST new parser to return the error "HDLCompiler:1821".
In ISE versions prior to 13.3, this code passes Synthesis and the 2-dimentional instantiation is interpreted as the following:
To resolve this error, instantiate individual gates separately.
You can also set the XST switch below to change the error to a warning and return to the ISE 13.2 behavior.